Siemens Standard Drives Application Handbook

1 Siemens Standard DrivesApplication HandbookMartin BrownSiemens Standard DrivesCongleton December 199721. What is a Variable Speed Drive?.. The Variable Frequency Siemens Standard Drives Product Product Selecting a Overall Supply Side Motor Load Acceleration and Braking Environmental Installing and Getting Started with an Mounting the Wiring up the First Switch If the motor does not Some Simple Applications and Using a Potentiometer with the Analog Using a Digital Using the Fixed Using other digital input Using the control current Limit and Protection Other Protection Some Additional

2 Electromagnetic Compatibility (EMC).. What is EMC?.. Minimising the problem of EMC Rules and Some Real A simple Fan A Closed Loop Controller using a Controlling Lift Door A Lift system for Industrial A Conveyer Application using several A Material Handling An Industrial Washing An Exercise Machine Advanced Applications Using Closed Loop Braking and Slowing down using Using the Serial Using Vector and FCC Options for Siemens Standard Clear Text Operating Panel Braking Modules and Braking RFI Suppression

3 PROFIBUS Input and Output APPENDIX 1: Using the USS Hardware Overview of the USS Message Detailed Description of the USS Protocol Examples of using the USS APPENDIX 2: Environmental Protection Levels (IP rating)..8812. APPENDIX 3: Some Useful manual is intended to help users of variable speed Drives successfully installand utilise Siemens Standard includes an introduction to Drives , which may be informative to first time users. Advanced information is shown in italics, and may be skipped on first technical information and complete parameter descriptions areavailable in the What is a Variable Speed Drive?

4 A Variable Speed Drive (VSD) consists of a Motor and some form of electric VSDs consisted of AC and DC motors combinations which wereused as rotating controllers. The first electronic controllers used Thyristor (SCR)Rectifiers which controlled the voltage, and therefore the speed of DC DC VSDs are still widely used and offer very sophisticated , the DC motor is large, expensive and requires periodic brushmaintenance. The AC induction motor is simple, low cost, reliable and widelyused throughout the order to control the speed of an AC induction motor a more complex controller,usually called an inverter is required.

5 In order to understand how an inverter works, it is necessary to understand howan induction motor induction motor works like a transformer. When the stator (the fixed, outerwinding) is connected to a three phase power source, a magnetic field whichrotates at the frequency of the supply is set 13213 Simplifed Induction Motor - Cross SectionStator WindingsAir GapRotor ShaftThis field crosses the air gap between the stator and rotor and causes currentsto flow in the rotor windings. This produces a force on the rotor as the currentinteracts with the changing magnetic field, and the rotor the windings are arranged in several pairs (or poles), the frequency of therotating field will be less than the applied frequency ( two pole = 50/60Hz =3000/3600rpm, but four pole = 50/60Hz = 1500/1800 rpm).

6 However, if the rotor runs at the same speed as the rotating field, there will be nochanging magnetic field, and therefore no torque. Therefore the rotor always runsa little slower than the rotating field in order to generate torque. This difference inspeed is known as OperatingPointTorque Speed Characteristic of An Induction MotorSlipPull out (Maximum) TorqueTorqueVariable frequency operationHence the speed of the motor depends on the applied frequency, as well as thewinding arrangement, and a little on the in order to control the motor speed it is necessary to control thefrequency of the the frequency is reduced, the voltage must be reduced or the magnetic flux willbe too high and the motor will saturate.

7 Hence the voltage must be controlled aswell. If the frequency is increased above normal, more voltage would normally beneeded to maintain maximum flux; this is not usually possible, so less torque isavailable at high , VoltageSpeed ( X 50/60)Torque Reduction above Base speedTorque CapabilityTherefore in order to control the speed of a Standard AC motor, the appliedfrequency and voltage must be it is difficult to control voltage and frequencies at these high powers, theuse of a Standard induction motor allows a cost effective speed control system tobe The Variable Frequency electronic converter which converts direct current (DC)

8 To Alternating current (AC) is known as an inverter. Electronic speed controllers for AC motors usuallyconvert the AC supply to DC using a rectifier, and then convert it back to avariable frequency, variable voltage AC supply using an inverter bridge. Theconnection between the rectifier and inverter is called the DC link. The blockdiagram of a speed controller (often called an inverter) is shown below:8 RectiferDC Link InverterSupply C+-CInverter Block DiagramThe supply, which can be single phase (usually at low power) or three phase isfed to a full wave rectifier which supplies the DC link capacitors.

9 The capacitorsreduce the voltage ripple (especially on single phase supplies) and supplyenergy for short mains breaks. The voltage on the capacitors is uncontrolled anddepends on the peak AC supply DC voltage is converted back to AC using Pulse Width Modulation (PWM).The desired waveform is built up by switching the output transistors (InsulatedGate Bipolar Transistors; IGBTs) on and off at a fixed frequency (the switchingfrequency). By varying the on and off time of the IGBTs the desired current canbe generated, but the output voltage is still a series of square wave pulses.

10 PulseWidth Modulation is shown in the figure Width ModulationVoltageCurrentThere are many complex aspects of inverters which need to be consideredduring the design:9 The control system to calculate the PWM requirements is very complex andspecially designed integrated circuits (ASICs) are needed. The control electronics are often connected to the DC link, which isconnected to the supply, so the customer connections, display etc. must besafely isolated from this. The output current must be carefully monitored to protect the inverter andthe motor during overload and short circuit.